how breathable a wind shell is

Nian,

A hard shell made with a porous membrane, such as eVent, provides “worst case rain protection” in combination with air permeability as high as .53 CFM. This is what I measured on the Integral Designs Thru Hiker. I measured the air permeability of the Rab Boreas windshirt, which Dave C. gave the highest rating in his recent SOTM report; at 68.69 CFM but with no external moisture protection. THE DIFFERENCE is 68.69 / .53 = 1,296%.

To put the windshirt air permeability spectrum in perspective, the most breathable windshirt I have measured is the 2007 version Acteryx Squamish at 100.59 CFM. The windshirt that will achieve the optimal balance point, for most people while UL backpacking, is the Houdini.

I measured the older Pertex Classic fabric and it was 3 CFM. Assuming this is the Pertex fabric used in your windshirt, it is a very poor choice for use while UL backpacking. I also measured the North Face Verto windshirt using the newest Pertex GL fabric and it was even worse at .53 CFM, the same as the Thru Hiker eVent. I then had a forum member, who purchases a lot of Pertex fabric, contact his rep. The rep's spec for the fabric was less than 1.97 CFM.

At a 7 MET exertion level (UL backpacking average), in average summer mountain temperatures and wind conditions, most people find the Houdini air permeability the optimal windshirt available. I measured the spring 2012 version of this windshirt at 35.8 CFM. The reason its air permeability is optimal is that this is the level of air permeability that will JUST PASS the AVERAGE EVAPORATED SWEAT moisture while UL backpacking. More air permeability than provided by the Houdini is not a wise choice for most people.

As air permeability goes up, wind resistance and external moisture protection goes down. More air permeability than is required to pass through your sweat is not a benefit. The key to selecting optimal windshirt air permeability is matching the air permeability that will just pass your average evaporated sweat level without venting. Venting can then be used for augmentation.

A windshirt that would never limit your maximum possible work potential requires ~400 CFM air permeability and would be worthless for protecting you from any wind or moisture. It is a balancing act.

@richard
by any chance did you ever measure the Montane Fetaherlight? is there a post here with more data RE other designs apart from the Houdini and Boreas?

10x
Mike

Mike,

I didn't measure the Montane Featherlight air permeability. Any article and most forum posts I have seen on BPL has provided only subjective windshirt air permeability ratings. Unfortunately, most manufacturers also do not provide air permeability test data.

You can roughly ball park a relative position estimate by comparing the windshirt you are interested in to one of the three low, medium, and high references, that I provided, using a “air suck test”.

@richard – unfortunately no real access to that type of gear here in israel :(

RE pertex – Montane uses "pertex microlight" – is that the classic?

RE Houdini – i assume that is the older model…i gather the new one is less permeable
Is the driclime similarly specd?

M

Richard,

Very interesting figures, you are a scientist :)

My pertex shell is Montane feather light smock. If it's only 3 CFM then may be it's not enough for me. Saw that Houdini a lot, maybe will get one. Do you by any chance test other material like Marmot driclime?

Thanks for those figures, very informative.

Nian

It should be breathable. I wear my sierra designs kenosha wind shirt while sleeping and I never wake up with damp clothes. I can't say that about sleeping with a rain jacket on.

I am going to pass on creating forum posts dealing with the testing of the less mainstream windshirts that were released in various years.

I tested the Houdini versions for these years:

2008 Houdini = 47.01
2009 Houdini = 43.85
2010 Houdini = 38.12
2011 Houdini (Military Special Edition) = 35.42
2012 Houdini (Spring Version) = 35.80

I tested the Marmot DriClime for only one model year:

2010 DriClime = 24.25

Both of these windshirt brands are near the sweet spot of air permeability required for UL backpacking but, the fixed thermal insulation layer of the DriClime limits its versatility.

One thing clear to me is the term "windshirt" is very nebulous without knowing the model / year / and its respective air permeability.

I thought that Dave did a good job on his two windshirt SOTM articles but, based on the published Boreas material specification; it was too porous, too heavy, and too prone to snagging to garner an "A" rating, for most people, in the spectrum of UL windshirts. I acquired one and lab tested it to see if how it compared to my preconceived notions.

Its air permeability tested about half way between the Houdini and Squamish. At that air permeability rating, its equivalent breathability competitors were the myriad Polartec Wind Pro jackets. Since those jackets weigh at least 2x more, I was forced to acknowledge that it could conceivably be considered UL relative to them with comparable weather resistance.

There is no magic windshirt; as air permeability goes up, external wind and water resistance goes down. Whichever windshirt just barely achieves the necessary moisture transport for your average MET (7 for backpacking) is the optimal solution.

For my personal backpacking use, a layered Houdini (with Velcro added to fix the big wrist problem) gets my A rating. The material used is an EPIC process which keeps the DWR active for the life of the garment. At 7 MET (backpacking average) it needs to transport ~8,000 – 10,000 g/m2/24 h which it does. In contrast, an eVent jacket can only transport about 5,000 g/m2/24. If you are a jock like Dave C. your average MET would be higher and hence the attractiveness of a garment like the Boreas.

For highly aerobic activities such as jogging, a layered Squamish would get my A rating. This option passes transports more body moisture and has better external wetness protection. The material is a weave in contrast to a knit like the Boreas; as a result it is much less prone to snagging during bush walks.

Thanks for the fantastic post, Richard.

Yet another example of "there is no single best ______ for ______".

Far too few product evaluations acknowledge the variability between individuals and also variability between different conditions. This one goes out of it's way to hilite those differences.

edit: "shoot first, aim later … kinda;-)" after posting I took the time to peruse the entire thread and … Richard has more than one post here that rates my appreciation.

"For my personal backpacking use, a layered Houdini (with Velcro added to fix the big wrist problem) gets my A rating. The material used is an EPIC process which keeps the DWR active for the life of the garment."

What do you mean by a "layered" Houdini? It is a term am unfamiliar with. Also, is the Houdini made with an EPIC style encapsulated thread?

Many thanks for your input.

Tom

In comparison to Richard's testing, after trying both the Houdini and Boreas, I found that I consistently overheated in the Houdini in moderately cool and windy temps. On the other hand, I have found the Boreas to be a perfect top for wearing by itself or layering while climbing, hiking, or running. Like Richard mentions, I think this is where personal preference, body chemistry, and climate come into play, as I run a little hot and don't choose a windshirt for its DWR.

Thanks Richard, I'm not a numbers guy (obviously), so your thoughts are highly valuable.

I did give the Houdini an A-, which I'd change to an A if the stock shell fit like my modified one. Having both is a nice quiver. The Houdini gets used a lot this time of year. A wool t-shirt, Cap 4 hoody, and Houdini is great for steady work in mixed weather (e.g. snowbiking and XC skiing during an intermittent snowstorm this weekend).

Pertex Classic (aka Pertex 5 or 6) is a lot heavier, and I assume less breathable, than either Microlight or Quantum. Good to do your research here.

Tom,

I used the term layered to differentiate the Houdini use from the DriClime in my prior post. I meant that I layered a different base layer under it based on the expected conditions versus always using a moderately thick layer under it like is built into the DriClime.

See http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=6696&skip_to_post=47736

Back in 2007 I first pointed out that my micrograph indicated that the threads were encapsulated as they are in the EPIC process.

I can post again – cool.

Personally, I find Gore-Tex to be one of the biggest scams around. It's breathable compared to a cheap PU coated raincoat, but it's not very breathable compared to a soft-shell. I've never been impressed by W/B fabrics since their inception in the late 1980s. My W/B jacket/pants stays in my pack and is only used when/if the weather turns foul.

I bought a Patagonia Houdini wind shirt in 2010 and it's probably the most versatile piece I own. It's DWR finish is excellent – will handle mist, very light rain, and snow. It's extremely breathable so you don't get hot and clammy like you do while wearing a W/B shell. For me, it excels when I'm doing things like climbing up a mountain on skis, where I need to break the bitter wind, but Gore-Tex will just roast me. It's the perfect garment. On a day where I'm doing a lot of up-hill climbing on skis or mountaineering, I'll wear Patagonia Guide Pants, syn underwear, syn base layer top, and the Patagonia Houdini jacket. When I stop, I'll toss on a parka.

In the summertime, if the weather window is looking decent, the houdini is all I'll carry for wind.

"I meant that I layered a different base layer under it based on the expected conditions versus always using a moderately thick layer under it like is built into the DriClime."

This and the link make things perfectly clear. As always.

Thanks again, Richard.

Thanks for the post Richard! I find myself needing to replace my Houdini. I was thinking about getting the Squamish from a feature perspective, now that I see the higher CFM, I am sure the Squamish will be my next windshirt given past experience comparing your and my comfort set point.

I don't suppose you have the CFM for Equilibrium used in the Rab Alpine Jacket Pullover?

–Mark

Mark,

Pertex specs that fabric at 10 CFM. The other Pertex fabrics I have tested were close to their specs.

Knowing how little insulation you require compared to me makes me think you would be happy with the Squamish.

> Pertex specs that fabric at 10 CFM.

Hmm… what confuses me is that my memory is that the Equilibrium in the Rab Alpine was more air permeable than my Houdini. Alas, I can't verify my memory because I sold my Rab Alpine and haven't yet purchased the smaller size yet.

–Mark

Richard,
Is that CFM for the current Squamish? Looks like there's a couple different names from different years of the fabric used (gossamera, luminera) and I'm wondering if it's still that breathable…

i have a celeris and i find it quite breathable …

windshirts are a mixed bunch … some are no more "breathable" than a good WPB … others are much more so …

the only way to find out is to test it in the store and outside … unless you have a book full of real testing ;)

it also depends on YOU and what you do … for example scrambling up a steep hill vs. prancing around some flat trails …

one question to ask is "do you really need a windshirt" … if its not that windy, you can usually get by even when cold with a light breathable fleece … if its really windy, youll get some cooling effect off that and one could just wear the WPB with zippers half open …

know your gear, test it, use it … dont think that you NEED any windshirt or any particular item because it is "popular" on BPL …

Numbers of CFM, provided by Richard Nisley do not correspond with "traditional" numbers, provided by manufacturers, etc. For example for Squamish it was 7 CFM, for traditional fleece – around 200 CFM and so on. In my simple unscientific test by blowing through the fabric Squamish was significantly less air permeable than fleece. And i thought Boreas (and similar MHW Chocklite) is more air permeable than Squamish. But i don't have Squamish right now to repeat test again. I am confused.

Great inputs from everyone. I can imagine a breathable wind shell can be useful a lot of time if not all the time and since it is so light. I will probably get a Houdini when I can get it on sale. Or a Rab celeris, or a Marmot ether driclime. I kind like the mesh vent on Marmot ether and it can be a midlayer under my shell since I will bring my shell anyway.

Roman,

Windshirt fabrics for the same model can change from year to year. Unlike the Houdini, I only checked one model year for the Sqamish. Polartec fleece types are a good reference because they are consistent. The classic fleece tests at 254 CFM and newer double face versions test at 325 CFM.

Brendan,

I have not tested any of the recent Squamish model years. Unlike the Hudouni, I don't know how the value changed for each model year. The one I tested has the Acteryx model listed as: Squamish Windshell – Men's – ARCTERYX; Item #: 202600; Price: Reg. $139.00. In their marketing description they called the fabric Gossamera nylon.

Don Wilson | 2008-04-08 14:49:00-06 reviewed the same windshirt in BPL. He described the breathability as, "I was pleased with the breathability of the fabric, which seemed on par with similar windshells. What I like best about the fabric is the soft drape and comfortable feel against my skin. The fabric is less smooth than the fabric in many lighter windshells, and doesn't make me feel like I am wearing a plastic bag."

I found that same air permeability in the Squamish Windshell as the MH Canyon shirt and the RR Adventure shirt. Both of these shirts are designed for summer use.